1. Field of the Invention
The present invention relates to a color conversion media, especially a color conversion media for use in electroluminescent displays.
2. Background Art
In principle, electroluminescent (EL) elements have a structure comprising an EL layer at least sandwiched between an anode and a cathode. In practice, methods used for constructing EL displays using EL elements include (1) a method in which EL elements, which respectively emit lights of three primary colors, are arranged, (2) a method in which an EL element, which emits white light, is used in combination with color filter layers for three primary colors, and (3) a method (CCM[color conversion medium] method) in which an EL element, which emits for example blue light for example, is used in combination with a CCM layer for converting a blue color to a green color and a color conversion layer for converting a blue/green color to a red color.
In the method (3) [CCM method], the use of only an EL element, which emits a light having higher energy than light to be converted, suffices for contemplated purposes. Therefore, unlike the EL display according to the method (1), there is no need to have properties of EL elements for respective colors, and, in addition, unlike the EL display according to the method (2), there is no drawback that, in color separation using color filters for the three primary colors, the utilization efficiency of white light is low. The method (3) [CCM method] enhances the conversion efficiency of the CCM layer to improve the brightness of the display.
Luminophors used for constituting the color conversion layer for converting blue to green and the color conversion layer for converting blue/green to red sometimes, however, undergo a deterioration, for example, due to external light and excitation light leaked from the adjacent color conversion layer. The former problem, that is, the problem of the deterioration due to the external light can be overcome, for example, by the interposition of a color filter layer between the color conversion layer and the transparent substrate as a support or the application of a ultraviolet light shielding film onto the transparent substrate. On the other hand, other measures should be taken for overcoming the latter problem, that is, the deterioration due to the leaked excitation light or the like.
It has hitherto been often pointed out that, due to the fact that the thicknesses of the color conversion layers are larger than the thickness of a light shielding layer (hereinafter referred to as “black matrix”) and vary from layer to layer, light incident to the color conversion layer having a relatively larger thickness causes scattering or the like and, leading to leakage of light to the adjacent color conversion layer. In order to prevent this phenomenon, Japanese Patent Laid-Open No. 241860/1998 proposes polishing the color conversion layers.
Even when the means, which polishes the color conversion layer together with the light shielding layer, is used, however, the final thicknesses of the color conversion layers should be made even. For this reason, due to the necessity of providing the light shielding layer in a thickness larger than the usually adopted thickness, the width of the light shielding layer should also be increased. Further, in forming the color conversion layers, in order to avoid mixing of mutually adjacent color conversion layer forming compositions, all the color conversion layers should be formed in a large height.